1. Field of the Invention
The present invention relates to an electrophotographic copier for copying originals onto an image receiving material by means of a photoconductor surface, and particularly to such a copier which uses films for transporting the originals through an exposing station wherein the individual original is inserted between these films.
2. Discussion of Related Art
There is a fundamental problem in carrying out the reproduction of technical drawings, particularly those used in design practice and in civil engineering and building activities, in highly automated copying machines, in that it is difficult to repetitively copy different drawing formats with nearly identical efficiencies. In the case of electrophotographic copiers, solutions such as using moving tables or moving mirrors for DIN A3 and A4 formats are adapted from the technology of office copiers. However, these solutions are transferable to electrophotographic copying equipment for processing the larger formats only at great expense.
German Auslegeschrift No. 2,026,063 discloses a sheet conveying apparatus for the purpose of moving originals which are to be copied, in particular originals of technical drawings, through the illumination and projection zone of a reproduction machine. This sheet conveying apparatus enables different length documents to be copied to be moved rapidly and repeatedly past the point at which they are processed. For this purpose, a conveying drum which can rotate in the conveying direction is located at the processing point. This drum has gripping devices which attach to the leading edge of the sheet. After having been attached to the sheet, the conveying drum is rotated through a predetermined angle and stopped, and an endless conveyor interacts with the conveying drum. This conveyor frictionally engages the sheet on the conveying drum and, once the conveying drum has stopped, displaces the sheet relative to the drum thus moving the rear portion of the sheet past the point at which it is to be processed. In a repetitive operation, the smallest format of a document moves in a circular motion without being guided, while larger formats are stopped and held in a loop, until the leading edge again sets them into motion. For this purpose, the original is securely held in a slot by means of a clamp. Using this system, it is impossible to expose the original with transmitted light, and it is consequently impossible to produce contact copies from the original. Furthermore, comparatively high design related expense is involved in providing the conveying drum with gripping devices.
A copying apparatus with a reflex-type exposing device is described in German Offenlegungsschrift No. 1,946,037, and likewise in U.S. Pat. No. 3,659,935, which apparatus arrangements are made to guide the image receiving material and the original in opposite directions, a short distance apart, at the end faces of a web-shaped glass fiber optical system. The original is guided along the exposing station between an optically transparent film and an endless belt.
The optically transparent film, the so-called spacing film, slides together with the original on the original side along one of the end faces of the glass fiber optical system. The film is then reversed at a roller and thereafter slides along the other end face of the glass fiber optical system, on the image receiving material side, together with the image receiving material. The transport of the original and of the image receiving material is thus effected only by a single film, which is wound and unwound onto and, as the case may be, from appropriate rollers. In this arrangement, it suffices to drive only one of the rollers. Although this copying apparatus is designed only for operation with reflex-type illumination, it can, however, also be employed for exposure with transmitted light. This copying apparatus has the disadvantage that the original is not held at a defined position, such as at its leading edge. Therefore, it is difficult to synchronize the original and the image receiving material when operating the copying apparatus in the repetitive mode.